The rapid determination of the nucleotide sequence of single- and double-stranded DNA and RNA is a major goal of researchers seeking to obtain the sequence for the entire genome of an organism. The ability to determine the sequence of nucleic acids in DNA or RNA has additional importance in identifying genetic mutations and polymorphisms. The concept of using nanometer-sized holes, or “nanopores,” to characterize biological macromolecules and polymer molecules has recently been developed.
Nanopore-based analysis methods often involve passing a polymeric molecule, for example single-stranded DNA (“ssDNA”), through a nanoscopic opening while monitoring a signal such as an electrical signal. Typically, the nanopore is designed to have a size that allows the polymer to pass only in a sequential, single file order. As the polymer molecule passes through the nanopore, differences in the chemical and physical properties of the monomeric units that make up the polymer, for example, the nucleotides that compose the ssDNA, are translated into characteristic electrical signals.
The signal can, for example, be detected as a modulation of the ionic current by the passage of a DNA molecule through the nanopore, which current is created by an applied voltage across the nanopore-bearing membrane or film. Because of structural differences between different nucleotides, different types of nucleotides interrupt the current in different ways, with each different type of nucleotide within the ssDNA producing a type-specific modulation in the current as it passes through a nanopore, and thus allowing the sequence of the DNA to be determined.
Nanopores that have been used for sequencing DNA include protein nanopores held within lipid bilayer membranes, such as α-hemolysin nanopores, and solid state nanopores formed, for example, by ion beam sculpting of a solid state thin film. Devices using nanopores to sequence DNA and RNA molecules have generally not been capable of reading sequence at a single-nucleotide resolution.
While this prior work has shown the promise of nanopores for detecting some sequence information, there is a need for accurate, reliable devices and methods for measuring sequences such as those of RNA and DNA. Accordingly, there is a need for a method of fabricating arrays of nanopores in a form that is amenable to manufacturing and can provide accurate and reliable measures of nanopore current. Similarly, there is a related need for devices capable of sequencing molecules having nanoscale dimensions at a high speed and at a high level of resolution.